Porous silicon has attracted more interest lately, especially due to its excellent properties related to applications in detectors and sensors, including gas sensors, humidity sensors, and biosensors, super capacitor, silicon-based optoelectronics, including electroluminescent displays and photodetectors, chemical and biological filters, and solar cells. In addition, porous silicon is also an ideal biomaterial due to its good biocompatibility for use in semiconductor optoelectronic devices linked to living tissues, its bioactive properties for medical implant, its non-toxic advantage over other semiconductors, its highly controllable properties by varying the porosity, and porosity dependent optical properties for medical imaging.
Additionally, in semiconductor manufacturing, a low-k dielectric is a material having a small dielectric constant compared to silicon dioxide. Low-k dielectric material implementation is one of several strategies used to allow the continued miniaturization of microelectronic devices. In digital circuits, insulating dielectrics separate the conducting parts, such as wire interconnects and transistors, from one another. As components have scaled and transistors have become spaced closer together, the thickness of the insulating dielectrics has decreased to the point where charge buildup and crosstalk adversely affects the performance of the device. Replacing silicon dioxide with a low-k dielectric material of the same thickness reduces parasitic capacitance, enabling faster switching speeds and lower heat dissipations.
One such low-k dielectric material is porous silicon dioxide. Air has a dielectric constant of roughly 1.0005, thus the dielectric constant of a material may be lowered by increasing the porosity of the material. Porous silicon dioxide may be formed by incorporating oxygen in a porous silicon layer.
Although porous silicon has been studied for over 30 years, there has not been much improvement in the growth technique since the invention of porous silicon. The widely used method to produce porous silicon is anodization. FIG. 1 shows the common method using to create porous silicon. A hydrogen fluoride (HF) solution 10 is prepared in a container 20, such as a Teflon container. A silicon substrate 30 is placed in the solution 10. A platinum cathode 40 is dipped into a hydrogen fluoride (HF) solution 10. The platinum cathode and the silicon substrate 30 are connected to the negative and positive sides of a power source 50, respectively. Current passing through the solution 10 allows the growth of porous silicon on the surface of the silicon substrate 30. The complicated fabrication steps and high fabrication cost are significant bottlenecks for the fabrication of new porous silicon-based devices. In addition, this process is not compatible with the standard silicon process. Further, this process can only be used to make crystalline porous silicon. For some applications, amorphous porous silicon may be required.
Therefore, there is a need for an improved method of creating porous materials, such silicon. Further, there is a need to control the formation of that silicon so that the pore size can be regulated. In addition, there is a need for an improved method of creating porous oxides, such as silicon dioxide.